When California suffered its biggest-ever mudslide on May 20, it lost a quarter of a mile of Highway 1 near to a terrifying torrent of rock and dirt.

But it also gained a massive 13 acres of coastline - the equivalent of ten football fields, comprising an estimated 71 million cubic feet of collapsed earth - the US Geological Survey (USGS) has revealed.

Scientists aren't just surprised by the sheer size of the area that was created - they're astonished that it was created at all, because the US usually loses coastline rather than gaining it.

'To witness the change of the coast in a constructional way - it's such a unique event,' landslide expert Kevin Schmidt of USGS in Menlo Park told the East Bay Times.

'Typically we are losing the battle to wave action,' said Schmidt, who wasn't involved in the USGS project. #It has been a number of decades since something this large increased our land mass.'

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The California coastline has expanded by 13 acres - the equivalent of ten football fields - after the Big Sur landslide on May 20. Some 70 million cubic feet of rock and soil fell from as high as 1,100 feet onto Highway 1

This quarter-mile stretch of Highway 1 - seen here before the collapse - was buried up to 80 feet beneath the displaced rock and soil. Experts say that adding to the coastline rather than having it erode is a rare phenomenon

Workers are now trying to clear the road and restore the Highway, although it's not expected to be completed for another year. Experts say the new coastline likely won't be permanent - it will probably erode over the coming years

The highway had already been closed to the public days before the landslide occurred because shifting hillsides had already been noted. Workers were evacuates when it became clear that a massive collapse was incoming, and nobody was hurt

USGS research geologist Jonathan Warrick, who is based in Santa Cruz, led the project, using aerial photos taken out of the window of a Cessna plane on May 27 to calculate the extent of the collapse.

He found that the equivalent of 2 million cubic meters of rock and dirt - that's 70 million cubic feet, or 200,000 dump trucks' worth of soil - had fallen on the road from as far as 1,100 feet above.

Whatever remains of Highway 1 is now buried under 80 feet of mountainside at its deepest point.

That's exciting for geologists, who are used to seeing America get smaller, not larger.

'There are only three places where we gain [land],' said Gary Griggs, professor of earth sciences and director of the Institute of Marine Sciences at UC Santa Cruz, and author of Living With the Changing California Coast.

'[They are] Hawaii, where new lava flows into the ocean, cools and we sell it for beachfront property; deltas, like the Mississippi, although that is low-lying; and then massive coastal landslides.'

But the said that the newly amassed land would be 'relatively short-lived... It might take a couple years or a decade, but it will erode.'

Authorities say it will take up to a year to reopen Highway 1.

The US Geological Survey (USGS) used photos taken of the ever-shifting area - close to Mud Creek - to track its changes over time. This photo is from a month and a half before the slide

This photo, taken a week after the slide, shows how immense the collapse was. It was likely due in part to heavy rain and snowfall experienced across California in its wettest winter in over a decade

The surprisingly wet winter broke the state's years-long drought but also caused floodings and landslides across the state. The Big Sur was the largest of these - indeed, the largest ever recorded in California

No-one had been hurt in the landslide, as the road had already been closed off to the public after earlier landslides in January.

A work crew had been in place on May 19 to perform repairs when it became clear that the hillside was shifting at a dangerous rate and a massive landslide was imminent.

'The success story is this: Caltrans sensed it was moving and got the crews out,' Warrick said, referring to the California Department of Transportation. 'Because of that, no one died.

'That type of movement wouldn't have been kind to people in the way. That is the untold story here. Some folks got the message, understood the magnitude of this thing and pulled the crews off.'

The massive landslide was the latest natural disaster to hit the California community, which relies heavily on the iconic coastal highway and tourism to survive.

It also added to a record $1 billion in highway damage that the state had endured after one of its wettest winters in in decades.

A roughly 30-mile stretch, between Mud Creek and Pfeiffer Canyon Bridge, was rendered isolated and accessible to tourists only by helicopter.

The wet winter - one of the rainiest and snowiest in California's history - broke a five-year drought, but also caused flooding and landslides across the state, and sped up coastal erosion.

This photo, taken das after the landslide, shows the swathe of road lost to the collapse. A 30-mile-long stretch of highway was cut off by the collapse and is now only accessible by helicopter

California's bill for environmental damages was already just over $1 billion before the collapse. The financial year for the state ends on June 30

The mudslide on the Pacific Coast Highway was the latest natural disaster to hit a California community that relies heavily on an iconic coastal highway and tourism to survive

'This type of thing may become more frequent, but Big Sur has its own unique geology,' said Dan Carl, a district director for the California Coastal Commission whose area includes Big Sur. 'A lot of Big Sur is moving; you just don't see it.'

Even before the weekend slide, storms across California caused just over $1 billion in highway damage to more than 400 sites.

The fiscal year for that total ends on June 30, Mark Dinger, also a spokesman for the state transportation agency, said at the time. The massive sum compares with $660 million last year.

Big Sur is one of the state's biggest tourist draws in a normal year, attracting visitors to serene groves of redwoods, beaches and the dramatic ocean scenery along narrow, winding Highway 1.

This winter has been particularly rough for Big Sur, state transportation spokesman Colin Jones said.

Repeated landslides and floods have taken out bridges and highways, closed campgrounds, and forced some resorts to shut down temporarily or use helicopters to fly in guests and supplies.

Big Sur is one of the state's biggest tourist draws in a normal year, attracting visitors to serene groves of redwoods, beaches and the dramatic ocean scenery along narrow, winding Highway 1